The Occupational Studies Section conducts epidemiologic studies to identify the occupational causes of cancer. Major areas of investigation include pesticides, organic solvents and other widely used chemicals, organic and inorganic dusts and methodologic investigations to improve exposure assessments. Studies of agricultural-related occupations uncovered elevated risks for lymphatic and hematopoietic cancer among farmers and flour millers. The excess of non-Hodgkin's lymphoma among farmers was strongly associated with use of the herbicide, 2,4-D. Excesses for certain lymphatic and hematopoietic tumors were also noted among Coast Guard marine inspectors exposed to a variety of chemicals while inspecting ships and barrages, among embalmers and funeral directors exposed to formaldehyde and other chemicals, and among dry cleaners having contact with perchloroethylene and petroleum solvents. Physical activity occurring on the job was associated with a reduced risk of colon cancer in two studies. Lung cancer was excessive among workers in hematite mines exposed to silica and radon, among workers exposed to chrome pigments, among workers engaged in the production of resins and molding compounds, and among persons exposed to motor vehicle exhausts. Major efforts underway include investigations of industrial workers exposed to acrylonitrile; workers in dusty trades exposed to silica; workers in China exposed to benzene; lawn care workers and agricultural applicators exposed to herbicides; embalmers exposed to formaldehyde, occupational and other causes of non-Hodgkin's lymphoma, multiple myeloma, and cancers of the brain, pancreas, and bladder; and workers in Turkey exposed to various industrial chemicals. Methodologic studies are being conducted to improve exposure assessment procedures and to develop a referent data base composed of workers.